The present invention relates to a stencil printer and more particularly to a stencil printer of the type including a multistage paper feeding device capable of feeding papers of different kinds and an ink drum shiftable in the widthwise direction of the papers perpendicular to a direction in which the papers are conveyed.
A digital stencil printer is conventional which uses a laminate thermosensitive stencil made up of a thermoplastic resin film and a porous support adhered to each other. The printer includes athermal head for selectively perforating, or cutting, the resin film of the stencil with heat in accordance with image data. After the perforated stencil or master has been wrapped around an ink drum, ink feeding means arranged in the drum feeds an adequate amount of ink to the inner periphery of the drum. A press roller, press drum or similar pressing member presses a paper or similar recording medium against the ink drum so as to transfer the ink from the drum to the paper via the porous portion of the drum and the perforations of the master. As a result, an image represented by the image data is printed on the paper. Usually, a paper feeding device for continuously feeding papers one by one is built in the printer. The paper feeding device generally includes a feed tray to be loaded with a stack of papers and a pair of side fences for guiding the papers in the widthwise direction of the papers.
With the above printer, it is possible to shift the position of an image on the paper in the widthwise direction of the paper perpendicular to the direction of paper conveyance by shifting the feed tray of the paper feeding device in the widthwise direction. However, the adjustment of the shift relying on eyesight and the manual shift of the feed tray cannot easily implement delicate adjustment or accurate adjustment. In light of this, Japanese Patent Laid-Open Publication No. 5-306025, for example, discloses an arrangement for automatically shifting the feed tray of the paper feeding device.
To meet various kinds of needs, a stencil printer including a multistage paper feeding device has recently been proposed. The multistage paper feeding device has a plurality of paper stocking portions and is capable of feeding papers of particular kind from each paper stocking portion. For such a multistage paper feeding device, Japanese Patent Laid-Open Publication No. 6-345281, for example, teaches an arrangement for automatically shifting a plurality of feed trays in the widthwise direction of the papers at the same time.
However, in any one of the conventional arrangements, a discharge tray for receiving papers, or printings, is not shiftable although the feed tray is shiftable. This brings about a problem that when the feed tray is shifted, the resulting printings cannot be accurately positioned on the discharge tray, and a problem that a pair of side fences on the discharge tray must be shifted independently of each other, obstructing easy operation. The arrangement taught in the above Laid-Open Publication No. 6-345281 has a drawback that a complicated construction is necessary for all of the feed trays to be shifted at the same time. Moreover, when the center of any one of the feed trays is deviated, the position of an image on a paper varies and must be adjusted every time the feed tray is selected.
Japanese Patent Laid-Open Publication No. 6-293175, for example, proposes an implementation for promoting accurate positioning of papers on the discharge tray, easy operation of the side fences of the discharge tray and simple construction. The implementation taught in this document is such that the feed tray and discharge tray are fixed in place while the ink drum is shiftable in the widthwise direction of papers. At the time of printing, the ink drum is shifted in the above direction for adjusting the position of an image on a paper.
A problem with the above Laid-Open Publication No. 6-293175 is that if the center line of any one of the feed trays included in the multistage paper feeding device is deviated, then the ink drum must be readjusted in position by troublesome operation every time the feed tray is selected. Another problem is that adjusting the center tray by tray is not practicable without resorting to highly accurate assembly, increasing the cost and reducing design freedom.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-40137, 10-1254, and 5-124737.
It is therefore an object of the present invention to provide a stencil printer capable of adjusting, when the center of any feed tray of a multistage paper feeding device is deviated, an image position on a paper easily and automatically without increasing the cost.
A stencil printer of the present invention includes a hollow cylindrical, porous ink drum freely rotatable. A multistage paper feeding device includes a plurality of paper stacking portions and capable of feeding papers of particular size from each paper stacking portion. At least one pair of side fences are mounted on each paper stocking portion for positioning the papers in the widthwise direction of the papers. A rack is positioned to stack the papers or printings each carrying a printed image thereon. An ink drum shifting device shifts the ink drum in the width wise direction of the papers perpendicular to the direction of conveyance of the papers. A rack shifting device shifts the rack in the widthwise direction of the papers. A storing device stores the position of a center line of a paper transport path for each of the paper stocking portions. A control section controls the operation of the ink drum shifting device and that of the rack shifting device in accordance with the position of the center line stored in the storing device.